I have had a second meter for almost 20 years. In the first 10 years, there was even an additional 15% on the discounted electricity. The basic fee was initially €50 and is now €90/a. Unfortunately, the price difference is currently so small that it no longer covers the basic fee. Overall, it was really worth it, especially because we had not yet brick-clad the house in the first 5 years (higher consumption). Due to a few changes, e.g. integration into Home Assistant, etc., consumption has decreased so much that today I would not install a second meter anymore. For a new building that probably requires significantly less electricity, it already seems uninteresting even without photovoltaics.